Connection device for electric accumulator

ABSTRACT

A connection device for an electric accumulator  10  a first connection subassembly  16  associated with one of the electrodes  12 . It comprises a metallic conducting strip  20  provided with several pins that will be embedded in the electrode  12  to make the electrical contact, and temperature and/or electrical protection means housed in a fixed module  25  electrically connected to one of the ends of the strip  20.

TECHNICAL DOMAIN OF THE INVENTION

The invention relates to a connection device for an electric accumulatorcomprising a first connection subassembly associated with one of theelectrodes, and a second connection subassembly associated with theother electrode.

STATE OF THE ART

Electrical connections for electric accumulators are usually made usingconnectors that are inserted into electrodes in the form of tabs, orscrew-on collars fixed to conducting contacts with opposite polarities.The reliability of the connection interface may be influenced bycorrosion or bad tightening, introducing a risk of increasing theelectrical resistance. The result is a large voltage drop that reducesthe electrical efficiency of the accumulator, and poor dissipation ofheat during operation of the accumulator.

PURPOSE OF THE INVENTION

The purpose of the invention is to make a connection device for anaccumulator in order to obtain high contact quality in the long term, alow voltage drop and protection against electrical overloads andabnormal temperature rises.

The device according to the invention is characterized in that the firstconnection subassembly comprises:

-   -   a metallic conducting strip provided with several pins that will        be embedded in the electrode to make the electrical contact,    -   and temperature and/or electrical protection means housed in a        fixed module electrically connected to one of the ends of the        strip.

According to one preferred embodiment, the pins are distributed over theentire surface of the strip that comes into contact with the electrode.Advantageously, the plane surface of the electrode is covered by a softconducting metal strip, particularly based on lithium, before pressureis applied to the strip to force it into place.

According to one special feature of the invention, the temperatureprotection means comprise a temperature switch activated by a statechange of a paste sensitive to a change in temperature, and return meansthat pull the switch towards the open position when the temperatureexceeds a predetermined limit.

According to one characteristic of the invention, the paste isconducting and is located within the contact gap of the temperatureswitch.

According to another special feature of the invention, the paste is madeof a material that melts under the action of heat.

The electrical protection means comprise an electrical switch comprisinga circuit breaker with a rated fuse, formed by a local restriction ofthe cross section of the conducting path of an electrical connectingpart.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics will become clearer from thefollowing description of an embodiment of the invention given as anon-limitative example illustrated in the appended drawings, wherein:

FIG. 1 shows a perspective diagrammatic view of three accumulatorelements equipped with the connection device according to the invention;

FIG. 2 shows a partial sectional view along the line 2-2 in FIG. 1,illustrating the first connection subassembly fixed to the anode of anaccumulator element;

FIG. 3 shows a larger scale view of a detail in FIG. 2;

FIGS. 4 and 5 show two example embodiments of the pin strip forming thefirst connection subassembly;

FIG. 6 shows an exploded perspective view of the protection moduleassociated with the top part of the pin strip;

FIG. 7 shows a vertical sectional view of FIG. 6 after assembly of theprotection module with the strip;

FIGS. 8 and 10 show perspective views illustrating two variantembodiments of the protection module;

FIG. 9 shows a sectional view along line 9-9 in FIG. 10.

DESCRIPTION OF A PREFERRED EMBODIMENT

Modular accumulator elements 10 are installed side by side whileremaining connected to an electrical connection device, as illustratedin FIGS. 1 to 3. The small opposite faces of each accumulator element 10are provided with a pair of plane electrodes 12, 14, called the anodeand the cathode respectively. The connection device is composed of afirst connection subassembly 16 associated with the anode of eachaccumulator element 10, and a second connection subassembly 18associated with the cathodes of the set of accumulator elements 10.

The first connection subassembly 16 of the anode is arranged to performan electrical contact resistance function, and a temperature and/orelectrical protection function. It comprises a rectangular metallicstrip 20 made of a conducting material, with an internal surface onwhich several pins 22 are formed. The first electrode 12 is covered by asheet 24 of soft metal, for example lithium, with which this strip 20comes into contact. The pins 22 are embedded into the first electrode12, and the soft metal of the sheet 24 deforms under the effect of themechanical pressure applied from the smooth outside face of the strip20, so as to create good contact between the anode and the firstconnection subassembly 16.

The pins 22 distributed on the internal surface of the conducting strip20 may be made by any process, particularly by stamping or perforating ametal sheet (FIGS. 2 and 3), by stamping (FIG. 4), dendritic depositionor chemical or electrochemical reaction (FIG. 5).

Good contact of the strip 20 on the anode guarantees electrical andthermal conductivity of the connection interface, firstly enabling theaccumulator element 10 to discharge with maximum electrical efficiency,and secondly dissipation of heat generated by the Joule effect due topermanent current circulation, or an internal defect.

In FIGS. 6 and 7, the protection means comprise a fixed moduleelectrically connected to the top end of the strip 20 and fitted with atemperature switch 26 and an electrical switch 27. According to a firstembodiment, the temperature switch 26 is composed of a conducting springstrip 28 and a contact gap filled with conducting paste 30 with apredetermined softening point that depends on the temperature. Thespring strip 28 forms a calibrated conducting spring inserted betweenthe strip 20 and a conducting connecting part 31 to which the load powersupply cable 32 is connected.

The conducting paste 30 in the interval between the curved end bracket34 of the strip 20 and the connecting part 31 remains in the solid stateas long as the temperature remains below the softening threshold. Mostof the nominal current that passes through the accumulator element 10passes through the conducting paste 30 without a significant voltagedrop, since the electrical resistance of the steel spring 28 is greaterthan the resistance of the paste 30.

If the temperature in the controlled area increases, the softeningthreshold of the paste 30 in the contact gap is exceeded causingexpansion of the steel strip spring 28, making the connecting part 31move along the direction of arrow F opening the contacts delimiting thecontact gap. The current then circulates in the steel strip spring 28,and its high electrical resistance reduces the current intensity. Thus,the temperature switch 26 protects the accumulator element 10 wheneverthe temperature rises due to an internal fault or incorrect use.

The electrical switch 27 in FIG. 6 is composed of a circuit breaker witha rated fused installed in series between the temperature switch 26 andthe output cable 32. For example, the fused circuit breaker may beformed by a local restriction of section 36 on the conducting path onthe connecting part 31. This narrowed section 36 melts due to the Jouleeffect as soon as the intensity of the current exceeds a given overloadthreshold.

The two contact gaps of the two switches 26, 27 are connected in seriesand are activated separately from each other. In one variant embodiment,it is clear that only one electrical breaking zone can be used toperform the temperature and electrical protection functions.

In FIG. 8, the temperature switch 26 comprises a sliding conductingsleeve 38, the end bracket 34 of the strip 20 fitting into one end andthe connecting part 31 fitting into the other end. The sleeve 38 acts asa conducting bridge between the end bracket 34 and the connecting part31, and a tension spring 40 is attached to the sleeve 38. Athermo-melting paste 42 holds the temperature switch 36 in the closedposition as long as the temperature remains below a predeterminedthreshold. If the temperature threshold is exceeded, the paste 42 meltsand the spring 40 moves the sleeve 38 in translation to open thetemperature switch 26.

In FIGS. 9 and 10, the temperature switch 26 is equipped with a springstrip 44 made of a conducting material that bears on the pin 44 and theconnecting part 31, through an intermediate thermo-melting material 42.As the material 42 melts, the circuit opens due to expansion of thespring strip 44. The electrical switch 27 is identical to that shown inFIG. 6.

In the three embodiments in FIGS. 7 to 10, the protection module 25 isinsert moulded in a rigid insulating material. The contact zones may beencased by a non-conducting insulating material 48, particularly wax,with a melting point below the melting point of the conducting paste 30,42 in the temperature switch 26.

According to one variant embodiment, the temperature and electricalprotections described above may be provided by a single component withan electrical resistance that depends on its internal temperature, forexample a positive temperature coefficient, or PTC, resistance in serieswith the strip 20. This type of component may change from a very lowinternal resistance to a sufficiently high resistance to limit orinterrupt the output current. The energy necessary for this state changemay originate either from the environment or the Joule effect.

The second connection subassembly 18 at the cathode end is shown inFIG. 1. The electrical contact between several accumulator elements 10and electrode 14 is made by welding of foil 50. The foil is shaped likebellows to enable transverse expansion, and foil elements areinterconnected through resistance plates 52. Welding of foil 50 toelectrodes 14 is facilitated by pre-tinning of contact areas 54.

1. A connection device for an electric accumulator comprising a firstexternal connection subassembly associated with a first electrode of theelectric accumulator, and a second external connection subassemblyassociated with a second electrode of the electric accumulator, thefirst external connection subassembly comprising: a first metallicconducting strip having several pins for being embedded in the firstelectrode to make electrical contact, and at least one of temperatureand electrical protection means housed in a fixed module electricallyconnected to one end of the strip.
 2. A connection device for anelectric accumulator according to claim 1, wherein a first surface ofthe first strip contacts the first electrode, and the pins aredistributed over the entire first surface of the first strip.
 3. Aconnection device for an electric accumulator according to claim 1,further comprising a second soft conducting metal strip covering asurface of the first electrode adjacent to the first strip.
 4. Aconnection device for an electric accumulator according to claim 3,wherein the second strip comprises lithium.
 5. A connection device foran electric accumulator according to claim 1, wherein temperatureprotection means comprise a temperature-sensitive paste and returnmeans, and when a temperature of the paste exceeds a predeterminedlimit, the return means pull the switch towards an open position.
 6. Aconnection device for an electric accumulator according to claim 5,wherein the conducting paste is located in a contact gap between thefirst strip and connector of a power supply cable.
 7. A connectiondevice for an electric accumulator according to claim 5, wherein thepaste comprises a material that melts under heat.
 8. A connection devicefor an electric accumulator according to claim 1, wherein the electricalprotection means comprise an electrical switch comprising a circuitbreaker with a rated fuse, the fuse comprising a local restriction of aconducting path between the first strip and an electrical connectingpart for connecting the first strip to an electrical power cable.
 9. Aconnection device for an electric accumulator according to claim 1,wherein the protection means comprise a positive temperature coefficientresistance in series with the first strip.
 10. A connection device foran electric accumulator according to claim 1, wherein the secondconnection subassembly comprises a foil welded to the second electrode,wherein the foil is welded to the second electrode after pre-tinning ofa contact area.
 11. A connection device for an electric accumulatorcomprising a first external connection subassembly associated with afirst electrode of the electric accumulator, and a second externalconnection subassembly associated with a second electrode of theelectric accumulator, the first external connection subassemblycomprising: a first metallic conducting strip having several pins forbeing embedded in the first electrode to make electrical contact, and atleast one of temperature and electrical protection means housed in afixed module electrically connected to one end of the strip; wherein asheet of soft metal is disposed between the first external connectionsubassembly and the first electrode, and wherein the sheet of soft metalis deformed by the pins of the first metallic conducting strip so thatthere is contact between the first external connection subassembly andthe first electrode.
 12. A connection device for an electric accumulatorcomprising a first external connection subassembly associated with afirst electrode of the electric accumulator, and a second externalconnection subassembly associated with a second electrode of theelectric accumulator, the first external connection subassemblycomprising: a first metallic conducting strip having several pins forbeing embedded in the first electrode to make electrical contact, and afixed module electrically connected to one end of the strip andcomprising a temperature switch and an electrical switch for protectingthe electric accumulator.
 13. A connection device for an electricaccumulator according to claim 12, wherein the temperature switch andthe electrical switch are a single component.